The initial deposition of 239Pu in the liver is independent of injected dose over the range 0.096 to 2.8μCi/kg. However, long term hepatic retention is a function of both the injected dose and time since injection. The rate of decrease is proportional to the early radiation dose rate to the liver. A similar effect was not observed in renal and splenic retention of 239Pu, The radiation dose rates to these tissues are considerably less than that to the liver.